Myopia (also called short-sight) is a common ocular condition in which distant objects appear blurred whereas near objects are seen clearly. Myopia often develops during childhood and typically increases in severity (requiring progressively stronger spectacles to correct it) until early adulthood, although the final amount of myopia that develops will vary between individuals.
Myopia is generally characterised by an abnormal enlargement of the eye-ball which has the effect of moving the light-sensitive tissue (the retina in the back of the eye) out of the focal plane of the optical components of the eye. Thus, images of distant objects are brought to focus in front of the retina, rather than in the plane of the retina. Images of distant objects are therefore seen as blurred. In high levels of myopia, the marked enlargement of the eye-ball also results in a stretching of the retina and its associated blood supply, which renders the eye more susceptible to retinal detachment, glaucomatous damage and degenerative myopic retinopathy.
The aetiology of myopia is poorly understood. Both genetic and environmental factors have been implicated and in susceptible individuals myopia progression is thought to be associated with excessive near work (eg reading, writing/drawing, playing video games, and similar), possibly because the prolonged muscular effort of focussing the eyes at near (accommodation) results in a lag of accommodation (insufficient accommodation) and hyperopic retinal de-focus. The correction of myopia requires minus-powered lenses which demand a greater accommodative effort for near work than is required without the lenses. This greater effort (and thus greater accommodative lag) has been implicated in exacerbating myopia progression.
International patent application WO2006/004440 discloses a method and contact lens for prevention of myopia progression. The contact lens includes a vision correction area for correcting in use the myopic vision of a wearer to present a clear image to the wearer during distance viewing, and during near viewing with accommodation by the eye during near viewing, and a myopic defocus area to also simultaneously present a myopic defocused image during both distance and near viewing (with accommodation by the eye during near viewing). The myopic retinal de-focus inhibits the abnormal axial elongation of the eyes that underlies myopia progression, with the effect that over time the progression of myopia slows, stops, or reverses.